I’m not surprised Vulcan is selling now. First of all, the Seattle market is one of the hottest in the country for commercial real estate investment.
Secondly, Vulcan spent years assembling contiguous real estate in South Lake Union so they could control the type of development that happened there when the market called for it. More specifically, they wanted to create a live/work environment with lots of mixed used development ie: retail (restaurants, shops, etc.) with condos, apartments, office, medical/life science uses, and hotels above. They didn’t want to build a nice office building with a restaurant below and then have somebody build a big warehouse or manufacturing facility next door. If it was all live/work then each piece is more valuable later. Not to mention that the neighborhood is better for the people who live there keeping rent/pricing high.
Now that one piece is fully developed and leased, they can sell it and use the cash to build on the next block when the market calls for it.